A matter of new life and cell death: programmed cell death in the mammalian ovary

BACKGROUND

The mammalian ovary is a unique organ that displays a distinctive feature of cyclic changes throughout the entire reproductive period. The estrous/menstrual cycles are associated with drastic functional and morphological rearrangements of ovarian tissue, including follicular development and degeneration, and the formation and subsequent atrophy of the corpus luteum. The flawless execution of these reiterative processes is impossible without the involvement of programmed cell death (PCD).

MAIN TEXT

PCD is crucial for efficient and careful clearance of excessive, depleted, or obsolete ovarian structures for ovarian cycling. Moreover, PCD facilitates selection of high-quality oocytes and formation of the ovarian reserve during embryonic and juvenile development. Disruption of PCD regulation can heavily impact the ovarian functions and is associated with various pathologies, from a moderate decrease in fertility to severe hormonal disturbance, complete loss of reproductive function, and tumorigenesis. This comprehensive review aims to provide updated information on the role of PCD in various processes occurring in normal and pathologic ovaries. Three major events of PCD in the ovary-progenitor germ cell depletion, follicular atresia, and corpus luteum degradation-are described, alongside the detailed information on molecular regulation of these processes, highlighting the contribution of apoptosis, autophagy, necroptosis, and ferroptosis. Ultimately, the current knowledge of PCD aberrations associated with pathologies, such as polycystic ovarian syndrome, premature ovarian insufficiency, and tumors of ovarian origin, is outlined.

CONCLUSION

PCD is an essential element in ovarian development, functions and pathologies. A thorough understanding of molecular mechanisms regulating PCD events is required for future advances in the diagnosis and management of various disorders of the ovary and the female reproductive system in general.

Effect of follicle-stimulating hormone and luteinizing hormone on apoptosis, autophagy, and the release and reception of some steroid hormones in yak granulosa cells through miR-23a/ASK1 axis

Follicle-stimulating hormone (FSH), luteinizing hormone (LH), miR-23a, apoptosis signal-regulating kinase 1(ASK1)/c-Jun N-terminal kinase (JNK), autophagy and apoptosis play crucial roles in follicular development. However, their role in yak granulosa cells (GCs) remains unknown. Therefore, we examined the effect of miR-23a, ASK1, FSH, and LH on apoptosis, autophagy, and the release and reception of some steroid hormones in these cells. Our results showed that miR-23a overexpression significantly increased the abundance of Beclin1, the LC3II/I ratio, and the number of Ad-mRFP-GFP-LC3-labeled autophagosomes, and decreased p62 abundance. Additionally, Bax abundance and the number of terminal deoxynucleotidyl transferase deoxynucleotide triphosphate nick end labeling-positive cells were reduced, while Bcl2 expression was increased. Overexpression of miR-23a also significantly increased the abundance of estradiol receptor α (ER-α) and β (ER-β) and the concentrations of estradiol (E2), progesterone (P4) in yak GCs. Here, treating yak GCs with miR-23a decreased ASK1 expression, which regulates ASK1/JNK-mediated apoptosis, autophagy, E2 and P4 levels, and ER-α/β abundance. In contrast, treatment of yak GCs with FSH (10 μg/mL) and LH (100 μg/mL) increased miR-23a abundance, regulating the subsequent effect on ASK1/JNK-mediated apoptosis, autophagy, ER-α/β abundance, and E2 and P4 concentrations. In conclusion, miR-23a enhances autophagy in yak GCs, attenuates apoptosis, and increases ER-α/β abundance and E2 and P4 concentrations by downregulating ASK1. Additionally, FSH and LH can regulate these effects of miR-23a by altering its expression. These results provide important insights that can inform the development of strategies to reduce abnormal follicular atresia and improve the reproductive rate of yaks.

Genistein ameliorates starvation-induced porcine follicular granulosa cell apoptosis

In brief

Genistein contributes to granulosa cell (GC) survival by two routes: one is that genistein induced p-AMPK and inhibited p-mTOR, which induces LC3 activation and autophagy; the other is that genistein inhibited caspase-3 and its cleavage, which induces PARP1 activation and PARylation.

Abstract

Genistein is an isoflavone which is beneficial for health, but little is known regarding its function on granulosa cell fate during follicular atresia. In the present study, we established an in vitro model of porcine follicular granulosa cell apoptosis by serum deprivation and showed that treatments with 1 μM and 10 μM genistein significantly reduced the apoptotic rate of granulosa cells compared to the blank control (P < 0.05). These results suggest that genistein at micromolar levels alleviates serum deprivation-induced granulosa cell apoptosis, and the ameliorative effect of genistein on granulosa cell apoptosis is likely to be able to inhibit nutrient depletion-induced follicular atresia. Further experimental results revealed that the expression of the autophagic marker protein LC3II in 100 nM-10 μM genistein treatment increased in a dose-dependent manner and was higher than the control (P < 0.05). Genistein also dose dependently promoted the phosphorylation of AMPK (adenosine 5'-monophosphate-activated protein kinase) in granulosa cells. Poly(ADP-ribose) (pADPr) formation in genistein-treated groups was also notably higher than in the controls (P < 0.05). Collectively, genistein alleviates serum deprivation-induced granulosa cells in vitro through enhancing autophagy, which involving AMPK activation and PARylation signaling. However, further study should be carried out to investigate the role of the aforementioned signaling on this process.

FSHR-mTOR-HIF1 signaling alleviates mouse follicles from AMPK-induced atresia

The majority of activated ovarian follicles undergo atresia during reproductive life in mammals, and only a small number of follicles are ovulated. Though hormone treatment has been widely used to promote folliculogenesis, the molecular mechanism behind follicle selection and atresia remains under debate due to inconsistency among investigation models. Using a high-throughput molecular pathology strategy, we depicted a transcriptional atlas of mouse follicular granulosa cells (GCs) under physiological condition and obtained molecular signatures in healthy and atresia GCs during development. Functional results revealed hypoxia-inducible factor 1 (HIF1) as a major effector downstream of follicle-stimulating hormone (FSH), and HIF1 activation is essential for follicle growth. Energy shortage leads to prevalent AMP-activated protein kinase (AMPK) activation and drives follicular atresia. FSHR-mTOR-HIF1 signaling helps follicles escape from the atresia fate, while energy stress persists. Our work provides a comprehensive understanding of the molecular network behind follicle selection and atresia under physiological condition.

Treatment of porcine ovarian follicles with tert-butyl hydroperoxide as an ovarian senescence model in vitro

Ovarian aging is the main reason of female reproductive problems. Excessive oxidative stress can induce ovarian senescence and follicular atresia, thereby reducing the reproductive performance. Follicles were divided into five groups for in vitro culture based on the duration of stimulation with tert-butyl hydroperoxide (t-BHP)-control group and groups 1 h, 2 h, 6 h, and 12 h. The results revealed that the ratio of progesterone (P4) to estradiol (E2) was increased after 24 and 36 h of follicle culture, shifting follicles toward atresia (P < 0.05). Stimulated by 200 μM t-BHP, follicles showed progressive aging phenotype. Senescence-associated β-galactosidase staining (SA-β-Gal) showed a significant increase in the number of positive cells (P < 0.05). Reactive oxygen species were also significantly upregulated (P < 0.05). t-BHP treatment for 6 h induced significant increases in Caspase 3, P53, and Foxo1 mRNA and protein levels (P < 0.05) and significant decreases in SOD mRNA and protein levels (P < 0.05). Transcriptome sequencing analysis of the follicles showed that the aged and treatment groups were clustered together in hierarchical clustering. Correlation analysis indicated significant changes at the transcriptome level in the treatment groups versus the control group. The common differentially expressed genes in the treatment groups were enriched in three growth-factor signaling pathways associated with cell proliferation and apoptosis (P53, mTOR, and MAPK). In conclusion, induction of follicular senescence by treatment with 200 μM t-BHP for 6 h is an effective in vitro model to simulate ovarian senescence in sows.

Silica Nanoparticles Promote Apoptosis in Ovarian Granulosa Cells via Autophagy Dysfunction

Although silica nanoparticles (SNPs) are generally thought to be biocompatible and safe, the adverse effects of SNPs were also reported in previous studies. SNPs cause follicular atresia via the induction of ovarian granulosa cell apoptosis. However, the mechanisms for this phenomenon are not well understood. This study focuses on exploring the relationship between autophagy and apoptosis induced by SNPs in ovarian granulosa cells. Our results showed that 25.0 mg/kg body weight (b.w.)/intratracheal instillation of 110 nm in diameter spherical Stöber SNPs caused ovarian granulosa cell apoptosis in follicles in vivo. We also found that SNPs mainly internalized into the lumens of the lysosomes in primary cultured ovarian granulosa cells in vitro. SNPs induced cytotoxicity via a decrease in viability and an increase in apoptosis in a dose-dependent manner. SNPs increased BECLIN-1 and LC3-II levels, leading to the activation of autophagy and increased P62 level, resulting in the blockage of autophagic flux. SNPs increased the BAX/BCL-2 ratio and cleaved the caspase-3 level, resulting in the activation of the mitochondrial-mediated caspase-dependent apoptotic signaling pathway. SNPs enlarged the LysoTracker Red-positive compartments, decreased the CTSD level, and increased the acidity of lysosomes, leading to lysosomal impairment. Our results reveal that SNPs cause autophagy dysfunction via lysosomal impairment, resulting in follicular atresia via the enhancement of apoptosis in ovarian granulosa cells.

Gestational exposure to phenanthrene induces follicular atresia and endocrine dyscrasia in F1 adult female

Epidemiological investigations and animal studies demonstrate a significantly positive relationship between polycyclic aromatic hydrocarbons (PAHs) exposure and reproductive disorders. However, few researches are focused on the reproductive toxicity of low-molecular-weight PAHs (number of benzene ring ≤ 3) which occupy a large part of PAHs. Phenanthrene (Phe), a typical low-molecular-weight PAH, is one of the most abundant PAHs detected in foods. In the present study, oral treatment with Phe at a human exposure related level during gestation (60 μg/kg body weight every three days, six times in total) induced reproductive disorders in F1 adult female mice: the number of antral follicles (an immature stage of follicular development) were significantly increased, while the maturation of oocytes was inhibited and aggravated follicular atresia was observed; the serum levels of luteinizing hormone (LH), testosterone and estradiol were significantly reduced; the receptor of follicle-stimulating hormone (FSHR) and aromatase in the ovary were significantly upregulated; transcriptome analysis demonstrated that the phosphatidylinositol 3-kinase and protein kinase B (PI3K/Akt) signal pathway was upregulated, and the calcium signal pathway was disturbed, which probably accounts for the exacerbated atresia of the growing follicles and the excessive consumption of follicles. The reproductive toxicity of low-molecular-weight PAHs could not be neglected.

circRNA-Mediated Inhibin-Activin Balance Regulation in Ovarian Granulosa Cell Apoptosis and Follicular Atresia

Ovarian granulosa cells (GC) play an essential role in the development and atresia of follicles. Emerging studies suggest that non-coding RNAs are involved in the regulation of GC apoptosis. Here, we aimed to analyze the function of ssc-circINHA-001, coded by the first exon of the inhibin subunit α gene (INHA), in resisting GC apoptosis and follicular atresia by enhancing the expression of the inhibin subunit β A (INHBA) through a cluster of miRNAs. A higher expression of ssc-circINHA-001 in healthy follicles compared to early atretic follicles was detected by qRT-PCR. Its circular structure was confirmed by RNase R treatment and reversed PCR. The function of ssc-circINHA-001 in GC resistance to apoptosis was detected by in vitro transfection of its si-RNA. Furthermore, the dual-luciferase reporter assay suggested that ssc-circINHA-001 adsorbed three miRNAs, termed miR-214-5p, miR-7144-3p, and miR-9830-5p, which share the common target INHBA. A low expression of ssc-circINHA-001 increased the levels of the free miRNAs, inhibited INHBA expression, and thus raised GCs apoptosis through a shift from the secretion of activin to that of inhibin. Our study demonstrated the existence of a circRNA–microRNAs–INHBA regulatory axis in follicular GC apoptosis and provides insight into the relationship between circRNA function and its coding gene in inhibin/activin balance and ovarian physiological functions.

Microanalysis of Fish Ovarian Follicular Atresia: A Possible Synergic Action of Somatic and Immune Cells

The present study describes in detail the morphological characteristics of the process of ovarian follicular atresia in Redbelly tilapia (Coptodon zillii) during the nonbreeding season using light and electron microscopy and immunohistochemistry. The follicular regression process was initiated with shrinkage and disintegration of the nuclear membrane of oocytes resulting in dispersing of chromatin within the ooplasm, followed by marked hyperplasia and hypertrophy of follicular and granulosa cells, which exhibited a strong phagocytic activity to engulf the liquefied yolk particles. Rodlet cells and granulocytes were recorded on the follicular wall and invaded the regressed follicles. Rodlet cells expressed a strong immunoreactivity to matrix metalloperoxidase (MMP-9) and α-smooth muscle actin, while neutrophils expressed a strong reactivity to Myeloperoxidase-3 (MPO). In the advanced stage of follicular atresia, the yolk was almost phagocytized and resorbed and the regressed follicle lost its integrity and appeared to be formed of a cellular mass of phagocytic cells. Transmission electron microscopy revealed the presence of neutrophils, eosinophils, and dendritic cells within the atretic follicle in between these phagocytic cells. Moreover, numerous lysosomes, granules, and phagosomes were observed within the cytoplasm of both phagocytic cells and granulocytes. Telocytes were also demonstrated within the highly thickened richly vascularized theca layer during the late stages of follicular atresia. Immunohistochemical staining for caspase-3 established the participation of apoptosis in the advanced stages of follicular regression. Immune cells, rodlet cells, and telocytes in combination with follicular cells play an essential role in follicular atresia. In conclusion, the present study provides a new evidence on the role of both somatic and immune cells in the phenomenon of ovarian follicular atresia in Redbelly tilapia (Coptodon zillii) during the nonbreeding season.

Increased melanomacrophage centres in the liver of reproductively dysfunctional female greater amberjack Seriola dumerili (Risso, 1810)

The greater amberjack Seriola dumerili is a new aquaculture fish that may display reproductive dysfunctions. During extensive follicular atresia, which is a common reproductive dysfunction in females during vitellogenesis, part of the reabsorbed yolk returns to the liver to be metabolized and recycled. Melanomacrophage centres (MMCs) are aggregates of macrophage-like cells that play a role in the destruction, detoxification and recycling of endogenous and exogenous materials, and have been associated with systemic stress. Wild and captive-reared greater amberjack were sampled in the Mediterranean Sea during two different phases of the reproductive cycle. The liver of reproductively dysfunctional captive-reared females sampled during the spawning season showed a high density of both MMCs and apoptotic cells. A weak liver anti-cytochrome P450 monooxygenase 1A immunoreactivity was observed, suggesting that the examined fish were not exposed to environmental pollutants. We propose that the observed increase in MMCs and apoptosis in captive-reared fish was related to the hepatic overload associated to the metabolism of yolk proteins reabsorbed during extensive follicular atresia. Since follicular atresia is a frequent physiological and pathological event in teleosts, we suggest that the reproductive state should be always assessed when MMCs are used as markers of exposure to stress or pollutants.

Abundances of autophagy-related protein LC3B in granulosa cells, cumulus cells, and oocytes during atresia of pig antral follicles

In mammals, apoptosis has been accepted as the type of programmed cell death (PCD) that occurs in ovarian follicles undergoing atresia. Results of recent studies, however, indicate autophagy may be an alternative mechanism involved in follicle depletion through independent or tandem actions with apoptosis. Western blotting and immunofluorescence procedures were used in the present study to investigate the abundances of LC3B protein in freshly collected granulosa cells (GCs), cumulus cells (CCs), and oocytes to evaluate whether autophagy is an important process of antral follicle atresia in sexually mature sows. Furthermore, apoptosis was analyzed using annexin V and TUNEL assays in the same cellular cohorts to evaluate the correlation between the two processes. Immunostaining results indicate autophagy was induced in the majority of GCs, CCs, and oocytes from early and advanced stage atretic follicles. The quantitative results of western blot analysis indicate there is a progressive increase (P <  0.05) in abundance of autophagy-related protein (LC3B-II) in these cells compared with cells in non-atretic follicles. Furthermore, there is confirmation that apoptosis occurs in the GCs of atretic follicles, thus indicating that in pigs apoptosis and autophagy are processes in GCs that regulate PCD and as a consequence antral follicle depletion. There was a greater abundance of LC3B-II in CCs and oocytes of atretic follicles, while apoptosis was not detected. It, therefore, is suggested that in these cells the two processes function independently, with autophagy having a cytoprotective rather than PCD mechanism of action.

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Down-regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d. total length of the sampled fish was 32.7 ± 3.1 cm and mean ± s.d. age was 6.2 ± 1.5 years. Measurements of atresia were performed using the 'profile method' with the intensity of atresia adjusted according to the 'dissector method' (10.6% adjustment; coefficient of determination was 0.675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down-regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.

Melanins as biomarkers of ovarian follicular atresia in the catfish Heteropneustes fossilis: biochemical and histochemical characterization, seasonal variation and hormone effects

Follicular atresia is a common feature of the vertebrate ovary that occurs at different stages of folliculogenesis and ovarian regression. It has physiological significance to maintain homeostasis and control fecundity, and ensure removal of post-ovulatory follicular remnants for preparing the ovary for the next cycle. Pigments appear late in the atretic process as indigestible waste formed out of the degradation of the oocytes, follicle wall and granulocytes. In the present study, pigment accumulation was demonstrated by Schmorl's and Perls' staining methods in the atretic ovarian follicles of Heteropneustes fossilis during follicular development and regression. Melanins were characterized spectrophotometrically for the first time in fish ovary. The predominant form is eumelanin, followed by pheomelanin and alkali-soluble melanin. Melanins showed significant seasonal variations with levels low in gonad resting phase, increasing to the peak in the post-spawning phase. The concentration of melanins increased time-dependently in post-ovulated ovary after human chorionic gonadotropin treatment. In the spawning phase, in vitro incubation of ovary slices with estradiol-17β or dexamethasone for 8 or 16 h decreased both eumelanin and pheomelanin levels time-dependently. The alkali-soluble melanin showed a significant decrease only in the dexamethasone group at 16 h. The results show that melanin assay can be used as a biomarker of follicular atresia in fish ovary, natural or induced by environmental toxicants.

Roles of SIRT1 in granulosa cell apoptosis during the process of follicular atresia in porcine ovary

Ovarian follicular atresia is characterized by granulosa cell apoptosis, however, the exact mechanism is still unclear. Sirtuin 1 (SIRT1) is a NAD(+)-dependent deacetylase, which is associated with apoptosis in several of cell types, but its exact role in ovarian granulosa cell apoptosis is not clearly defined. In present study, we identified the involvement of SIRT1 in the process of follicle degeneration, which is known as "follicular atresia", both from in vivo models and cell culture data. The results of immunohistochemistry showed that SIRT1 was widely detected in non-apoptotic granulosa cells of follicles, but significantly decreased during the process of granulosa cell apoptosis. Quantitative real-time PCR and Western blot analysis showed that the expression levels of SIRT1 mRNA and protein were increased (P<0.05) during follicular atresia. In order to provide more evidences elucidating the roles of SIRT1 during the process of follicular atresia, granulosa cells were cultured in vitro with resveratrol which acts as a potent activator of SIRT1. Results showed that resveratrol caused a dose-dependent increase in both SIRT1 mRNA and protein levels. Meanwhile, apoptotic rate of granulosa cell was increased (P<0.01) in a dose-dependent manner. Additionally, resveratrol significantly increased the expression levels of Caspase-3 (P<0.01) and Bax mRNA (P<0.01), while Bcl-2 mRNA level was significantly decreased (P<0.01). Thus, our results suggest that SIRT1 may play important roles in the regulation of granulosa cell apoptosis during follicular atresia in porcine ovary.

Female reproductive aging is master-planned at the level of ovary

The ovary receives a finite pool of follicles during fetal life. Atresia remains the major form of follicular expenditure at all stages since development of ovary. The follicular reserve, however, declines at an exponential rate leading to accelerated rate of decay during the years preceding menopause. We examined if diminished follicle reserve that characterizes ovarian aging impacts the attrition rate. Premature ovarian aging was induced in rats by intra-embryonic injection of galactosyltransferase-antibody on embryonic day 10. On post-natal day 35 of the female litters, either a wedge of fat (sham control) or a wild type ovary collected from 25-day old control rats, was transplanted under the ovarian bursa in both sides. Follicular growth and atresia, and ovarian microenvironment were evaluated in the follicle-deficient host ovary and transplanted ovary by real time RT-PCR analysis of growth differentiation factor-9, bone morphogenetic protein 15, and kit ligand, biochemical evaluation of ovarian lipid peroxidation, superoxide dismutase (SOD) and catalase activity, and western blot analysis of ovarian pro- and anti-apoptotic factors including p53, bax, bcl2, and caspase 3. Results demonstrated that the rate of follicular atresia, which was highly preponderant in the follicle-deficient ovary of the sham-operated group, was significantly prevented in the presence of the transplanted ovary. As against the follicle-deficient ovary of the sham-operated group, the follicle-deficient host ovary as well as the transplanted ovary in the ovary-transplanted group exhibited stimulated follicle growth with increased expression of anti-apoptotic factors and down regulation of pro-apoptotic factors. Both the host and transplanted ovaries also had significantly lower rate of lipid peroxidation with increased SOD and catalase activity. We conclude that the declining follicular reserve is perhaps the immediate thrust that increases the rate of follicle depletion during the final phase of ovarian life when the follicle reserve wanes below certain threshold size.

Angiopoietin 1 reduces rat follicular atresia mediated by apoptosis through the PI3K/Akt pathway

The aim of this study was to determine the effect of the local inhibition of ANGPT1 on steroid production, proliferation and apoptosis of ovarian follicular cells and on the PI3K/AKT pathway. We also examined the effect of ANGPTs on follicular cell apoptosis and proliferation in early antral follicles (EAFs) in culture. Follicular cells expressing PCNA decreased after ANGPT1 Ab treatment. Moreover, ANGPT1 inhibition increased the levels of active caspase 3 and androsterone, but decreased estradiol, AKT phosphorylation and the area of smooth muscle cell actin. In cultured EAFs from prepubertal rats treated with diethylstilbestrol (DES), ANGPT1 increased PCNA and decreased apoptosis while ANGPT2 reversed these effects. These results show that ANGPT1 alters steroidogenesis, reduces ovarian apoptosis, and stimulates cell proliferation in antral follicles. ANGPT1 may exert these roles by regulating ovarian vascular stability and/or by a direct effect on follicular cells, possibly involving the PI3K/AKT pathway.

Disruption of the salmon reproductive endocrine axis through prolonged nutritional stress: changes in circulating hormone levels and transcripts for ovarian genes involved in steroidogenesis and apoptosis

Mechanisms regulating the normal progression of ovarian follicular growth versus onset of atresia in fishes are poorly understood. To gain a better understanding of these processes, we exposed immature female coho salmon (Oncorhynchus kisutch) to prolonged fasting to induce follicular atresia and monitored body growth, development of the ovarian follicles, changes in reproductive hormones, and transcripts for ovarian genes. Prolonged fasting reduced body and ovary weight and increased the appearance of atretic follicles relative to normally fed controls. Endocrine analyses showed that fasting reduced plasma insulin-like growth factor 1 (IGF1), estradiol-17β (E2), and pituitary, but not plasma, levels of follicle-stimulating hormone (FSH). Transcripts for ovarian fsh receptor (fshr) and steroidogenesis-related genes, such as steroidogenic acute regulatory protein (star), 3β-hydroxysteroid dehydrogenase (hsd3b), and P450 aromatase (cyp19a1a) were significantly lower in fasted fish. Ovarian expression of apoptosis-related genes, such as Fas-associated death domain (fadd), caspase 8 (casp8), caspase 3 (casp3), and caspase 9 (casp9) were significantly elevated in fasted fish compared to fed fish, indicating that apoptosis is involved in the process of atresia in this species. Interestingly, some genes such as fadd, casp8, casp3, and hsd3b, were differentially expressed prior to increases in the number of atretic follicles and reductions in hormone levels induced by fasting, and may therefore have potential as early indicators of atresia. Together these results suggest that prolonged nutritional stress may disrupt the reproductive system and induce follicular atresia in part via reductions in ovarian IGF and FSH signaling, and downstream effects on steroidogenesis-related genes and E2 production.

Apotosis in ovary

Folliculogenesis is a complex process involving dramatic morphological and functional changes in granulosa and theca cells. This process is sequential and dictated specifically by tightly regulated response to endocrine hormones and intra-ovarian regulators. In mammalian ovaries, only a few number of presented follicles in a fetal ovary can reach ovulatory status during follicular development; more than 99% of the follicles in the ovary undergo a degenerative process known as "atresia" induced by apotosis. It is characterized by distinct biochemical and morphological changes such as DNA fragmentation, plasma membrane blebbing and cell volume shrinkage. Apoptosis in ovary is regulated by a number of endocrine, locally produced intracellular mediators in a stage-specific and time-dependent manner. New knowledge of hormones and cell factors which regulate granulosa cell or oocyte apoptosis and their possible signaling pathways underlying intracellular events has made important contributions in advancing our understanding mechanism of follicular atresia.

A thrombospondin-mimetic peptide, ABT-898, suppresses angiogenesis and promotes follicular atresia in pre- and early-antral follicles in vivo

Using a novel in vitro angiogenesis assay, we previously showed that thrombospondin (TSP)-1 has antiangiogenic effects on rat follicles and induces apoptosis in granulosa cells in vitro. ABT-898 is an octapeptide mimetic of TSP-1 closely related to ABT-510. Here, we demonstrate the inhibitory effects of ABT-898 on follicular angiogenesis and its proapoptotic effect on granulosa cells. To investigate the potential of this peptide to inhibit follicular angiogenesis in vivo, marmoset monkeys were treated with 2.5 mg/kg ABT-898 twice daily throughout the follicular phase of the cycle. Although treatment did not block emergence of dominant follicles, angiogenesis was reduced in preantral and early-antral follicles. Furthermore, the incidence of atresia at these follicle stages was increased. To investigate whether treatment with ABT-898 would interfere with the timing or duration of the normal ovulatory rise in plasma progesterone, marmosets were treated with a depot formulation containing 25 mg ABT-898 at the start of the follicular phase, with a second injection after 2 wk. Despite active concentrations of peptide being maintained in the circulation, no apparent effects on the ovulatory cycle were observed. Taken together, these results indicate that ABT-898 is capable of having a dual effect by inhibiting follicular angiogenesis and promoting atresia of antral follicles in vivo but does not prevent ovulation or induce luteolysis, as has been observed with direct vascular endothelial growth factor inhibitors. These results suggest that ABT-898 could be a novel therapeutic to inhibit abnormal angiogenesis and induce atresia of accumulated follicles in polycystic ovary syndrome.

Thrombospondin-1 inhibits angiogenesis and promotes follicular atresia in a novel in vitro angiogenesis assay

Thrombospondin-1 (TSP-1) is a putative antiangiogenic factor, but its role in regulating physiological angiogenesis is unclear. We have developed a novel in vitro angiogenesis assay to study the effect of TSP-1 on follicular angiogenesis and development. Intact preantral/early antral follicles dissected from 21-d-old rat ovaries were cultured for 6 d in the presence or absence of TSP-1. At the end of the culture period, angiogenic sprouting from the follicles was quantified using image analysis. Follicles were fixed and sectioned, and follicular apoptosis was assessed by immunohistochemistry for activated caspase-3 in granulosa cells. The results showed that TSP-1 inhibited follicular angiogenesis (P < 0.01) and promoted follicular apoptosis (P < 0.001) in a dose-dependent manner. To determine whether the proapoptotic activity of TSP-1 is mediated by direct effects on granulosa cells, isolated granulosa cells were cultured with TSP-1 (0, 10, 100, and 1000 ng/ml) for 48 h. Apoptosis was quantified using a luminescent caspase-3/7 assay. TSP-1 promoted apoptosis of granulosa cells in a dose-dependent manner (P < 0.05), suggesting that TSP-1 can act independently of the angiogenesis pathway to promote follicular apoptosis. These results show that TSP-1 can both inhibit follicular angiogenesis and directly induce apoptosis of granulosa cells. As such, it may have potential as a therapeutic for abnormal ovarian angiogenesis and could facilitate the destruction of abnormal follicles observed in polycystic ovary syndrome.

Oogenesis in teleosts: how eggs are formed

One of the major objectives of the aquaculture industry is the production of a large number of viable eggs with high survival. Major achievements have been made in recent years in improving protocols for higher efficiency of egg production and viability of progeny. Main gaps remain, however, in understanding the dynamic processes associated with oogenesis, the formation of an egg, from the time that germ cells turn into oogonia, until the release of ova during spawning in teleosts. Recent studies on primordial germ-cells, yolk protein precursors and their processing within the developing oocyte, the deposition of vitamins in eggs, structure and function of egg envelopes and oocyte maturation processes, further reveal the complexity of oogenesis. Moreover, numerous circulating endocrine and locally-acting paracrine and autocrine factors regulate the various stages of oocyte development and maturation. Though it is clear that the major regulators during vitellogenesis and oocyte maturation are the pituitary gonadotropins (LH and FSH) and sex steroids, the picture emerging from recent studies is of complex hormonal cross-talk at all stages between the developing oocyte and its surrounding follicle layers to ensure coordination of the various processes that are involved in the production of a fertilizable egg. In this review we aim at highlighting recent advances on teleost fish oocyte differentiation, maturation and ovulation, including those involved in the degeneration and reabsorption of ovarian follicles (atresia). The role of blood-borne and local ovarian factors in the regulation of the key steps of development reveal new aspects associated with egg formation.

Regulation of angiotensin type 2 receptor in bovine granulosa cells

Angiotensin II (AngII) is best known for its role in blood pressure regulation, but it also has documented actions in the reproductive system. There are two AngII receptors, type 1 (AGTR1) and type 2 (AGTR2). AGTR2 mediates the noncardiovascular effects of AngII and is expressed in the granulosa cell layer in rodents and is associated with follicle atresia. In contrast, expression of AGTR2 is reported to occur only in theca cells in cattle. The objective of the present study was to determine whether AngII also plays a role in follicle atresia in cattle. RT-PCR demonstrated AGTR2 mRNA in both granulosa and theca cells of bovine follicles. The presence of AGTR2 protein was confirmed by immunofluorescence. Abundance of AGTR2 mRNA in granulosa cells was higher in healthy compared with atretic follicles, whereas in theca cells, it did not change. Granulosa cells were cultured in serum-free medium, and treatment with hormones that increase estradiol secretion (FSH, IGF-I, and bone morphogenetic protein-7) increased AGTR2 mRNA and protein levels, whereas fibroblast growth factors inhibited estradiol secretion and AGTR2 protein levels. The addition of AngII or an AGTR2-specific agonist to granulosa cells in culture did not affect estradiol secretion or cell proliferation but inhibited abundance of mRNA encoding serine protease inhibitor E2, a protein involved in tissue remodeling. Because estradiol secretion is a major marker of nonatretic granulosa cells, these data suggest that AngII is not associated with follicle atresia in cattle but may have other specific roles during follicle growth.

Expression and localization of the serine proteases high-temperature requirement factor A1, serine protease 23, and serine protease 35 in the mouse ovary

Proteolytic degradation of extracellular matrix components has been suggested to play an essential role in the occurrence of ovulation. Recent studies in our laboratory have indicated that the plasminogen activator and matrix metalloproteinase systems, which were previously believed to be crucial for ovulation, are not required in this process. In this study we have used a microarray approach to identify new proteases that are involved in ovulation. We found three serine proteases that were relatively highly expressed during ovulation: high-temperature requirement factor A1 (HtrA1), which was not regulated much during ovulation; serine protease 23 (PRSS23), which was down-regulated by gonadotropins; and serine protease 35 (PRSS35), which was up-regulated by gonadotropins. We have further investigated the expression patterns of these proteases during gonadotropin-induced ovulation in immature mice and in the corpus luteum (CL) of pseudopregnant mice. We found that HtrA1 was highly expressed in granulosa cells throughout follicular development and ovulation, as well as in the forming and regressing CL. PRSS23 was highly expressed in atretic follicles, and it was expressed in the ovarian stroma and theca tissues just before ovulation. PRSS35 was expressed in the theca layers of developing follicles. It was also highly induced in granulosa cells of preovulatory follicles. PRSS35 was also expressed in the forming and regressing CL. These data suggest that HtrA1 and PRSS35 may be involved in ovulation and CL formation and regression, and that PRSS23 may play a role in follicular atresia.

Immunohistochemical localization of galectin-3 in the reproductive organs of the cow

The protein levels and immunohistochemical localization of galectin-3, which is a beta-galactoside-binding protein, were studied in the cow reproductive organs. Using Western blot analysis, galectin-3 was detected at low levels in the ovary and oviduct, at moderate levels in the uterus, and at high levels in the cervix. Using immunohistochemistry, galectin-3 was immunolocalized in macrophages in the interstitium, in cells in the atretic follicles, and in luteal cells in the regressing corpus luteum, but not in the growing follicles in the ovary. In the oviduct, galectin-3 was detected in some macrophages in the lamina propria, submucosa and muscle layers, as well as in some cells in the covering epithelium. In the uterus, galectin-3 was immunolocalized in some epithelial cells and in some macrophages in the submucosa, but not in the endometrial glands at the non-pregnant stage. In the cervix, galectin-3 was immunolocalized in many mucus-secreting cells in the mucosa and in a few macrophages in the submucosa and muscle layers. Based on its localization, we postulate that galectin-3 in the covering epithelium is involved in the mucosal defense system, and that galectin-3-positive macrophages in all tissues are involved in either cell survival or death. In addition, galectin-3 plays an important role in the regression of follicles and the corpus luteum.

Role of nitric oxide on the generation of atretic follicles in the rat ovaries

The aim of this study was to investigate the role of Nitric Oxide (NO) in the atresia of ovarian follicles in an animal model. Twenty adult, female rats (90 days old with body weights of210 +/- 10 g in the beginning of the experiments) were divided into 4 groups of 5 each. They were treated twice daily from the subcutaneous route for 21 successive days with either of the following chemicals: nitroglycerine, L-arginine, L-NAME, or saline. On day 22, all animals were sacrificed. Ovaries were dissected out free of connected tissue and were fixed in formaline 10%. Later, paraffine blocks were prepared and serial sections were made by means of H and E routine staining method. Intact and atretic follicles were counted separately. In addition, damages were analyzed qualitatively from the points of view of appearance and morphologic changes. In the evaluation of ovarian follicular structures, different types of healthy as well as atretic follicles were observed. In most of atretic follicles, the oocytes were abnormally elongated and increnation of their outlines were obvious. There were numerous macrophages around and inside of the atretic follicles. Our investigation regarding the distribution of atretic follicles in the ovaries of test groups revealed that atretic follicles in the L-NAME treated group were increased in comparison to the control group. Conversely, however, in the arginine-treated group, the atretic follicles were reduced compared to the control animals. Treatment with nitroglycerine of the rats decreased the number of atretic follicles significantly (p < 0.05) in comparison to the control group. In conclusion, enhanced NO, either from endogenous or exogenous origins, prevents atresia phenomenon, while inhibition of NO exerts an opposite effect.

High Transcript Level of Fatty Acid-Binding Protein 11 but Not of Very Low-Density Lipoprotein Receptor Is Correlated to Ovarian Follicle Atresia in a Teleost Fish (Solea senegalensis)1

Transcripts encoding a fatty acid-binding protein (FABP), Fabp11, and two isoforms of very low-density lipoprotein receptor (Vldlr; vitellogenin receptor) were characterized from the ovary of Senegalese sole (Solea senegalensis). Phylogenetic analyses of vertebrate FABPs demonstrated that Senegalese sole Fabp11, as zebrafish (Danio rerio) homologous sequences, is part of a newly defined teleost fish FABP subfamily that is a sister clade of tetrapod FABP4/FABP5/FABP8/FABP9. RT-PCR revealed high levels of vldlr transcript splicing variants in the ovaries and, to a lesser extent, in somatic tissues, whereas fabp11 was highly expressed in the ovaries, liver, and adipose tissue. In situ hybridization analysis showed vldlr and fabp11 mRNAs in previtellogenic oocytes, whereas no hybridization signals were detected in the larger vitellogenic oocytes. Transcript expression of fabp11 was strongly upregulated in somatic cells surrounding atretic follicles. Real-time quantitative RT-PCR demonstrated that ovarian transcript levels of vldlr and fabp11 had a significant positive correlation with the percentage of follicles in previtellogenesis and atresia, respectively. These results suggest that the expression level of vldlr transcripts may be used as a precocious functional marker to quantify the number of oocytes recruited for vitellogenesis and that fabp11 mRNA may be a very useful molecular marker for determining cellular events and environmental factors that regulate follicular atresia in fish.

Effects of follicular atresia and size on the developmental competence of bovine oocytes: A study using the well-in-drop culture system

The effect of granulosa cell (GC) apoptosis and follicle size on the competence of bovine oocytes were studied using a well-in-drop (WID) oocyte/embryo culture system, which allows identification of follicular origin. Hatching rates of blastocysts did not differ (P>0.05) between oocytes cultured in the WID system (13%) and those cultured in the conventional group system (16%). Hatching rates of blastocysts were higher (P<0.05) in early atretic (17%) than in non-atretic (8%) and late atretic follicles (10%) of the same size (4-8mm), and in 6-8mm (22%) than in 4-5mm follicles (15%) at the early atretic stage. More oocytes (P<0.05) from late atretic (17%) than from non-atreteic (7%) or early atretic follicles (9%) of the same size (4-8mm) were arrested at Grade 1 cumulus expansion (only cells in the peripheral two layers began to expand). Similarly, more oocytes from 2 to 3mm follicles (30%) than from 6 to 8mm follicles (21%) at the same (late) atretic stage had Grade 1 cumulus expansion (P<0.05). Hatching blastocyst percentages of oocytes with Grade 3 (all layers of the cumulus except corona radiate cells expanded) or Grade 4 (full) cumulus expansion were higher in early atretic (20%) than in non-atretic (13%) or late atretic follicles (12%). Hatching blastocyst percentages of oocytes from follicles at the early atretic stage increased as cumulus expanded from Grade 2 (9%) to Grade 4 (27%). Regardless of the degree of follicle atresia, 72-76% of the floating cells in the follicular fluid (FF) were undergoing apoptosis. The floating cell density in FF was highly (r=0.6-0.7) correlated with oocyte developmental potency. In conclusion, the WID culture system was as efficient as group culture and allowed identification of follicular origin. Furthermore, the developmental potential of oocytes was affected by GC apoptosis, follicle size and cumulus expansion, and the floating cell density in FF could be used as a simple and non-invasive marker of oocyte quality.

Increased oocyte degeneration and follicular atresia during the estrous cycle in anti-Müllerian hormone null mice

Anti-Müllerian hormone (AMH) plays an important role in folliculogenesis. AMH null mice display an increased recruitment of primordial follicles. Nevertheless, these mice do not have proportionally more preovulatory follicles. Therefore, AMH null mice provide an interesting genetic model to study the regulation of species-specific number of preovulatory follicles. We studied the follicle pool throughout the estrous cycle at 4 months of age. Analysis of the follicle pool revealed that AMH null mice have an increased and earlier cyclic recruitment of growing follicles despite a blunted FSH surge at estrus. However, FSH levels at estrus were apparently too low to support growth to the preovulatory stage because an increased level of atresia was observed, which neutralized the increased cyclic recruitment. When AMH null mice were subjected to a superovulation scheme, the rise in FSH levels resulted in the rescue of the recruited cohort of growing follicles. Analysis of the follicle pool also revealed that the increased recruitment of primordial follicles in AMH null mice was neutralized by an increased loss of follicles during the transition from small preantral to large preantral follicle. This major loss of follicles was not completely reflected by a corresponding augmentation of atresia but did correspond with an increased number of oocyte remnants observed in AMH null mice. We conclude that a combination of increased oocyte degeneration and increased follicular atresia neutralizes the increased initial and cyclic recruitment in AMH null mice to a normal number of preovulatory follicles.

Prolonged survival in culture of preantral follicles from polycystic ovaries

CONTEXT

In polycystic ovary syndrome (PCOS), an increased proportion of follicles leave the primordial (resting) pool and initiate growth. However, there is little evidence for a reduced reproductive life span (early menopause) in women with PCOS, suggesting that the dynamics of follicle growth, and of follicle loss by atresia, is altered in PCOS.

OBJECTIVE

The aim of this study was to investigate the possibility that loss of preantral follicles by atresia is reduced in PCOS, leading to prolonged follicle survival.

DESIGN

We compared follicle growth in normal and polycystic ovaries using cultures of small ovarian biopsies.

SETTING

Tissue samples were obtained at routine laparoscopy from 12 patients with anovulatory PCOS and 16 controls and processed in an ovarian physiology laboratory.

MAIN OUTCOME MEASURES

We performed morphometric analysis of follicle population in tissue fixed at time of biopsy (d 0) or after 5, 10, or 15 d in culture. Analyses included assessment of follicle and oocyte diameter, number and proportion of primordial and growing follicles, and number and proportion of atretic follicles.

RESULTS

In tissue fixed on d 0, the proportion of healthy growing follicles was, as expected, greater in ovaries from PCOS patients than in normal ovaries (64 vs. 28%; P = 0.0005), but there were no differences between PCOS and normal tissue during culture. The rate of atresia throughout the period of culture in follicles was, however, significantly lower in PCOS tissue (P < 0.0001). After culture, 80% of follicles in normal ovarian tissue were atretic compared with 53% in PCOS biopsies.

CONCLUSION

Follicles from polycystic ovaries demonstrate a decreased rate of atresia in culture, suggesting a mechanism for maintaining a larger follicle pool throughout reproductive life.

Expression pattern of prokineticin 1 and its receptors in bovine ovaries during the estrous cycle: involvement in corpus luteum regression and follicular atresia

Prokineticin 1 (PROK1), also termed endocrine gland-derived vascular endothelial growth factor (endocrine gland-derived VEGF), is a newly identified protein assigned with diverse biologic functions. It binds two homologous G protein-coupled receptors, PROKR1 and PROKR2. To better understand the roles of PROK1 and its receptors in ovarian function, their expression was determined in follicles and corpora lutea (CLs) at different developmental stages. PROK1 mRNA levels were low at early luteal stage and midluteal stage, but increased sharply during natural or induced luteolysis. High PROK1 mRNA levels also were found in atretic follicles. This profile of PROK1 expression was opposite to that of the well-established angiogenic factor VEGF. Of the two receptor-type expressions, PROKR1 but not PROKR2 was correlated positively with its ligand. Immunohistochemical staining revealed that PROK1 was located mainly within the muscular layer of arterioles, and during regression it also was localized to macrophages and steroidogenic cells. The expression pattern of ITGB2 mRNA, a leukocyte cell marker, overlapped that of PROK1, thus suggesting that leukocyte infiltration may explain the elevated expression of PROK1 in atretic follicles and regressing CL. Indeed, flow cytometry analyses showed that nearly all beta-2 integrin chain (ITGB2)-positive cells also were stained with anti-PROK1 and that significantly more ITGB2/PROK1 double-stained cells were present in degenerating follicles and CL. Furthermore, when challenged in vitro with PROK1, adherent, mononuclear cell numbers and TNF levels were elevated, indicating that PROK1 triggers monocyte activation. Together, these data suggest that PROK1, acting via PROKR1, may be involved in the recruitment of monocytes to regressing CL and atretic follicles and their consequent activation therein.

Molecular Cloning of Porcine (Sus scrofa) Tumor Necrosis Factor Receptor 2

Tumor necrosis factor (TNF) alpha can induce both cell death and proliferation by binding to either TNF receptor (TNFR) 1 or 2. In the granulosa cells of porcine ovaries, TNFalpha is considered to act as an anti-apoptotic/survival factor during follicular atresia. As a first step toward elucidating the function of TNFR2 in regulating follicular development/growth and atresia in porcine ovaries, we isolated the porcine (Sus scrofa) cDNA encoding TNFR2, which was identified from a cDNA library prepared from the follicular granulosa cells of pig ovaries. Porcine TNFR2 (1,125 bp, 375 amino acid residues), which contains specific amino acid region of transmembrane, indicated high identities with human and murine TNFR2 (78 and 69% at mRNA level, respectively; 73 and 61% at protein level, respectively), suggesting that the function of porcine TNFR2 is similar to that of human and murine homologues. Understanding the expression patterns of porcine TNFR2 mRNA in various organs, which we confirmed by reverse transcription polymerase chain reaction analysis, would help to elucidate the physiological role of TNFR2 in the regulation of apoptosis in porcine organs.

The Role of Interleukin-6 in the Regulation of Granulosa Cell Apoptosis During Follicular Atresia in Pig Ovaries

More than 99% of follicles in mammalian ovaries undergo a degenerative process known as atresia, and only a few follicles actually ovulate during follicular growth and development. Follicular selection mostly depends on granulosa cell apoptosis, but the molecular mechanism behind the regulation of this selective atresia is still largely unknown. In the present study, to examine whether or not interleukin-6 (IL-6), a multifunctional cytokine, is involved in apoptosis during atresia in pig ovaries, the expression of IL-6 mRNA in granulosa cells was quantified by real-time reverse transcription-polymerase chain reaction (RT-PCR). The level of mRNA decreased during atresia. Enzyme-linked immunosorbent assay (ELISA) showed that the level of IL-6 protein in follicular fluid also decreased during atresia. Moreover, recombinant human IL-6 upregulated the expression of an intracellular apoptosis inhibitor, cellular FLICE-like inhibitory protein long form (cFLIP(L)), in cultured cells derived from human granulosa cells. It is possible that IL-6 is produced in the granulosa cells of healthy follicles, that it increases the cFLIP(L) level, and cFLIP(L) then prevents apoptotic cell death.

Changes in Expression of Interleukin-6 Receptors in Granulosa Cells During Follicular Atresia in Pig Ovaries

More than 99% of follicles undergo a degenerative process known as "atresia" in mammalian ovaries, and only a few follicles ovulate during follicular growth and development. Follicular selection predominantly depends on granulosa cell apoptosis. To reveal the molecular mechanisms of selective follicular atresia, we examined the changes in the levels of interleukin-6 (IL-6) receptors expressed in the granulosa cells of pig ovaries. The levels of IL-6 receptor (IL-6R)-alpha mRNA and protein in granulosa cells were quantified by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively. IL-6R alpha mRNA and protein were highly expressed in the granulosa cells of progressed atretic follicles. Enzyme-linked immunosorbent assay showed that the expression of IL-6 soluble receptor (IL-6sR) protein in follicular fluid decreased during atresia. Moreover, we isolated porcine cDNA encoding an IL-6 signal transducer, gp130. Porcine gp130 (2,754 bp and 917 amino acids) was identified from a cDNA library prepared using follicular granulosa cells of pig ovaries. Porcine gp130 was highly homologous with human and murine gp130. RT-PCR analysis revealed that the level of gp130 mRNA also decreased during atresia. We presume that IL-6sR and gp130, but not IL-6R alpha, play important roles in regulation of granulosa cell survival.

BAX is involved in regulating follicular growth, but is dispensable for follicle atresia in adult mouse ovaries

Mammalian females are endowed with a finite number of primordial follicles at birth or shortly thereafter. Immediately following the formation of the primordial follicle pool, cohorts of these follicles are recruited to begin growth, and this recruitment continues until the primordial follicle population is depleted. Once recruited, a follicle will either grow and ovulate or undergo atresia. Follicle atresia results from the apoptotic death of follicular cells. Members of the BCL-2 family of proteins are important regulators of apoptosis in most cells including in the ovary. Here, we tested the hypothesis that the proapoptotic BAX is an important regulator of follicle survival. We used a variety of histological and biochemical techniques to investigate the impact ofBaxdeletion on follicle growth and death. We observed that theBaxdeletion results in delayed vaginal opening and altered follicular growth. Young adultBax-deficient ovaries contained increased numbers of primordial follicles and a trend towards reduced numbers of growing follicles.Baxdeficiency led to a reduction in average litter size, and also a reduction in the number of oocytes ovulated in response to exogenous gonadotropins. In contrast,Baxdeficiency did not alter follicle atresia. In conclusion, BAX appears to be an important regulator of follicle growth, but is dispensable for follicle atresia in mice.

Short photoperiod-induced ovarian regression is mediated by apoptosis in Siberian hamsters (Phodopus sungorus)

Siberian hamster reproduction is mediated by photoperiod-induced changes in gonadal activity. However, little is known about how photoperiod induces cellular changes in ovarian function. We hypothesized that exposing female hamsters to short (inhibitory) as opposed to long (control) photoperiods would induce an apoptosis-mediated disruption of ovarian function. Ovaries and plasma from hamsters exposed to either long (LD, 16 h light:8 h darkness) or short (SD, 8 h light:16 h darkness) days were collected during diestrus II after 3, 6, 9 and 12 weeks and processed for histology or RIA respectively. Apoptosis was assessed by in situ TUNEL and active caspase-3 protein immunolabeling. No significant differences were observed among LD hamsters for any parameter; therefore, these control data were pooled. SD exposure induced a decline in preantral follicles (P < 0.05), early antral/antral follicles (P < 0.01) and corpora lutea (P < 0.01) by week 12 as compared with LD. Terminal atretic follicles appeared by SD week 9; by week 12, these had become the predominant ovarian structures. Estradiol concentrations decreased by weeks 9 and 12 SD when compared with both LD and week-3 SD hamsters (P < 0.05); however, no changes were observed for progesterone. TUNEL-positive follicles in SD ovaries increased at week 3 and subsequently declined by week 12 as compared with LD ovaries (P < 0.01). Active capsase-3 protein immunostaining peaked at SD week 3 as compared with all other groups (P < 0.01). TUNEL and capsase-3 immunolabeling were localized to granulosa cells of late-preantral and early-antral/antral follicles. These data indicate that SD exposure rapidly induces follicular apoptosis in Siberian hamsters, which ultimately disrupts both estradiol secretion and folliculogenesis, resulting in the seasonal loss of ovarian function.

Hormonal induction of ovulation stimulates atresia of antral follicles in a vespertilionid bat, Scotophilus heathi

Scotophilus heathi is a seasonally monoestrous subtropical vespertilionid bat found at Varanasi, India. Although the antral follicles remain present in the ovaries of S. heathi from November till March, ovulation is delayed in this species until early March. In order to understand the mechanism of ovulation suppression during this period of delayed ovulation, the effects of human chorionic gonadotropin (hCG), pregnant mare's serum gonadotropin (PMSG), follicle stimulating hormone (FSH) and gonadotropin releasing hormone agonist (GnRH agonist) on ovarian morphology and steroid concentration were investigated. Hormonal treatments were given as a single i.p. dose 24 h after capture. The bats were sacrificed 48 h after the injection. Treatment with hCG, PMSG, FSH and GnRH agonist failed to induce ovulation in S. heathi, although these hormones produced a high degree of ovarian stimulation. The administration of hCG and PMSG induced ovarian enlargement, intense hyperemia, marked changes in the interstitial cells (ICs), development of several antral follicles and a varying degree of abnormalities in the oocytes of most of the antral follicles. In the bats treated with hCG, PMSG and GnRH agonist, androstenedione concentration increased significantly to extraordinarily high levels, whereas estradiol concentration decreased. Administration of FSH caused regression of ICs and pyknosis of granulosa cells in the majority of antral follicles. FSH did not enhance androstenedione concentration. The results of the present study suggest that the failure of hormonal treatments to induce ovulation during the period of delayed ovulation might be due to a seasonal desensitization of ovarian follicles in S. heathi. The hormonal treatment instead stimulated the ICs to produce a high level of androstenedione resulting in atretic changes of the antral follicles.

A Morphological and Immunohistochemical Study of Healthy and Atretic Follicles in the Ovary of the Sexually Immature Ostrich (Struthio camelus)

The morphology of healthy and atretic follicles in the ovary of the sexually immature ostrich was described in the present study. In addition, the distribution of the intermediate filaments desmin, vimentin and smooth muscle actin, in these ovarian follicles, was demonstrated. Healthy and atretic primordial, pre-vitellogenic and vitellogenic follicles were present in the ovaries of the sexually immature ostrich. Atresia occurred during all stages of follicular development. Atretic primordial and pre-vitellogenic follicles were characterized by the presence of a shrunken oocyte surrounded by a multilayered granulosa cell layer. Two forms of atresia (types 1 and 2) were identified in vitellogenic follicles. In the advanced stages of type 1 atresia the follicle was dominated by a hyalinized mass. In contrast, in type 2 atresia the granulosa and theca interna cells differentiated into interstitial gland cells. Positive immunostaining for desmin was observed in the granulosa cells of only healthy primordial and pre-vitellogenic follicles. Atretic primordial and pre-vitellogenic follicles were immunonegative for desmin. Vimentin immunoreactivity was demonstrated in the granulosa cells of all follicles except the vitellogenic atretic follicles. The results of the present study indicate that ovarian follicles in the sexually immature ostrich undergo a cycle of growth and regression, which is similar to that reported in other avian species. Furthermore, based on the results of the immunohistochemical study, it would appear that the distribution and immunostaining of intermediate filaments changes during follicular development and atresia.

Methoxychlor Inhibits Growth and Induces Atresia of Antral Follicles through an Oxidative Stress Pathway

The mammalian ovary contains antral follicles, which are responsible for the synthesis and secretion of hormones that regulate estrous cyclicity and fertility. The organochlorine pesticide methoxychlor (MXC) causes atresia (follicle death via apoptosis) of antral follicles, but little is known about the mechanisms by which MXC does so. Oxidative stress is known to cause apoptosis in nonreproductive and reproductive tissues. Thus, we tested the hypothesis that MXC inhibits growth and induces atresia of antral follicles through an oxidative stress pathway. To test this hypothesis, antral follicles isolated from 39-day-old CD-1 mice were cultured with vehicle control (dimethylsulfoxide [DMSO]), MXC (1-100 microg/ml), or MXC + the antioxidant N-acetyl cysteine (NAC) (0.1-10 mM). During culture, growth was monitored daily. At the end of culture, follicles were processed for quantitative real-time polymerase chain reaction of Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX), and catalase (CAT) mRNA expression or for histological evaluation of atresia. The results indicate that exposure to MXC (1-100 microg/ml) inhibited growth of follicles compared to DMSO controls and that NAC (1-10 mM) blocked the ability of MXC to inhibit growth. MXC induced follicular atresia, whereas NAC (1-10 mM) blocked the ability of MXC to induce atresia. In addition, MXC reduced the expression of SOD1, GPX, and CAT, whereas NAC reduced the effects of MXC on their expression. Collectively, these data indicate MXC causes slow growth and increased atresia by inducing oxidative stress.

Growth differentiation factor 9 is antiapoptotic during follicular development from preantral to early antral stage

Ovarian follicular atresia represents a selection process that ensures the release of only healthy and viable oocytes during ovulation. The transition from preantral to early antral stage is the penultimate stage of development in terms of gonadotropin dependence and follicle destiny (survival/growth vs. atresia). We have examined whether and how oocyte-derived growth differentiation factor 9 (GDF-9) and FSH regulate follicular development and atresia during the preantral to early antral transition, by a novel combination of in vitro gene manipulation (i.e. intraoocyte injection of GDF-9 antisense oligos) and preantral follicle culture. Injection of GDF-9 antisense suppressed basal and FSH-induced preantral follicle growth in vitro, whereas addition of GDF-9 enhanced basal and FSH-induced follicular development. GDF-9 antisense activated caspase-3 and induced apoptosis in cultured preantral follicles, a response attenuated by exogenous GDF-9. GDF-9 increased phospho-Akt content in granulosa cells of early antral follicles. Although granulosa cell apoptosis induced by ceramide was attenuated by the presence of GDF-9, this protective effect of GDF-9 was prevented by the phosphatidylinositol 3-kinase inhibitor LY294002 and a dominant negative form of Akt. Injection of GDF-9 antisense decreased FSH receptor mRNA levels in cultured follicles, a response preventable by the presence of exogenous GDF-9. The data suggest that GDF-9 is antiapoptotic in preantral follicles and protects granulosa cells from undergoing apoptosis via activation of the phosphatidylinositol 3-kinase/Akt pathway. An adequate level of GDF-9 is required for follicular FSH receptor mRNA expression. GDF-9 promotes follicular survival and growth during the preantral to early antral transition by suppressing granulosa cell apoptosis and follicular atresia.

Role and regulation of nodal/activin receptor-like kinase 7 signaling pathway in the control of ovarian follicular atresia

Although the role of the TGF beta superfamily members in the regulation of ovarian folliculogenesis has been extensively studied, their involvement in follicular atresia is not well understood. In the present study, we have demonstrated for the first time that Nodal, a member of the TGF beta superfamily, is involved in promoting follicular atresia as evidenced by the following: 1) colocalization of Nodal and its type I receptor Activin receptor-like kinase 7 (ALK7) proteins in the granulosa cells was only observed in atretic antral follicles, whereas they were present in theca cells and granulosa cells of healthy follicles, respectively; 2) addition of recombinant Nodal or overexpression of Nodal by adenoviral infection induced apoptosis of otherwise healthy granulosa cells; 3) constitutively active ALK7 (ALK7-ca) overexpression mimicked the function of Nodal in the induction of granulosa cell apoptosis. Furthermore, overexpression of Nodal or ALK7-ca increased phosphorylation and nuclear translocation of Smad2, decreased X-linked inhibitor of apoptotic proteins (Xiap) expression at both mRNA and protein level and phospho-Akt content, as well as triggered mitochondrial release of death proteins Smac/DIABLO, Omi/HtrA2, and cytochrome c in the granulosa cells. Dominant-negative Smad2 significantly attenuated ALK7-ca-induced down-regulation of Xiap and thus rescued granulosa cells from undergoing apoptosis. In addition, whereas up-regulation of Xiap significantly attenuated ALK7-ca-induced apoptosis, down-regulation of Xiap sensitized granulosa cells to ALK7-ca-induced apoptosis. Furthermore, ALK7-ca-induced apoptosis was significantly attenuated by forced expression of activated Akt, and Akt rescued granulosa cells from undergoing apoptosis via proteasome-mediated ALK7 degradation. Taken together, Nodal plays an atretogenic role in the ovary where it induces granulosa cell apoptosis through activation of Smad2, down-regulation of the key survival molecules Xiap and phospho-Akt, as well as the activation of mitochondrial death pathway.

Effect of duration of dosing on onset of ovarian failure in a chemical-induced mouse model of perimenopause

OBJECTIVE

Repeated daily dosing with 4-vinylcyclohexene diepoxide (VCD) causes gradual ovarian failure in mice. As a result, the animal undergoes ovarian failure, but retains residual ovarian tissue. The purpose of this study was to use a mouse model to regulate the induction of a period analogous to perimenopause in women.

DESIGN

Female B6C3F1 mice (28 days old; n = 8) were dosed daily for 10 or 20 days with VCD (160 mg/kg/d) or sesame oil. The animals were evaluated for reproductive function on days 10, 20, 35 after the onset of dosing, and on the day of follicle depletion. Each animal was killed at the specified time points, and ovaries, uteri, and plasma were collected.

RESULTS

VCD reduced (P < 0.05) the number of primordial (by 93.2%) and primary (by 85.1%) follicles after 10 days of dosing, whereas essentially all primordial and primary follicles were lost (P < 0.05) after 20 days of dosing. The average time to ovarian failure was on day 135 for 10-day-dosed mice and on day 52 for 20-day-dosed mice. Follicle-depleted mice in both groups had decreased (P < 0.05) ovarian and uterine weights. Circulating follicle-stimulating hormone levels were increased (P < 0.05) on day 44 after the onset of dosing in 10-day-dosed mice and on day 35 in 20-day-dosed mice.

CONCLUSION

These results demonstrate that ovarian failure can be caused by VCD more rapidly if repeated daily dosing occurs for a longer period. Thus, the length of time leading up to ovarian failure (model for perimenopause) can be adjusted by varying the length of exposure.

Eggs forever?

A group of scientists from Harvard Medical School (Johnson et al., 2004) claims to have "established the existence of proliferative germ cells that sustain oocyte and follicle production in the postnatal mammalian ovary," expressing no doubts about their methods, results and conclusion. Johnson et al. based their conclusions of oocyte and follicular renewal from existing germline stem cells (GSC) in the postnatal mouse ovary on three types of observations: (1) A claimed discordance in follicle loss versus follicle atresia in the neonatal period and in the following pubertal and adult period; (2) immunohistochemical detection of proliferating GSC with meiotic capacity using combined markers for meiosis, germline, and mitosis; and (3) neo-folliculogenesis in ovarian chimeric grafting experiments with adult mice. Oogenesis is the process that transforms the proliferative oogonium into an oocyte through meiosis, followed by folliculogenesis and follicular and oocyte maturation. The most crucial part in producing a functional oocyte is firstly, initiation and completion of the first meiotic prophase, and secondly, enclosure of the resulting diplotene oocyte in a follicle. Neither of these two events has been shown to take place in Johnson et al.'s study of the postnatal mouse ovary. We hereby address the observations underpinning their hypothesis and conclude that it is premature to replace the paradigm that adult mammalian neo-oogenesis/folliculogenesis does not take place.

Follicular atresia during Dacus oleae oogenesis

Programmed cell death, constitutes a common fundamental incident that occurs during oogenesis in a variety of different animals. It plays a significant role in the maturation process of the female gamete and also in the removal of abnormal and superfluous cells at certain checkpoints of development. In the present study, we demonstrate the existence of follicular atresia during mid-oogenesis in the olive fruit fly Dacus oleae (Tephritidae). The number of atretic follicles increases following the age of the fly, suggesting for the presence of an age-susceptible process. The atretic follicles contain nurse cells that exhibit chromatin condensation, DNA fragmentation and actin cytoskeleton alterations, as revealed by propidium iodide staining, TUNEL labeling and phalloidin-FITC staining. Conventional light and electron microscopy disclose that the nurse cell remnants are phagocytosed by the adjacent follicle cells. The follicular epithelium also eliminates the oocyte through phagocytosis, resulting to an egg chamber with no compartmentalized organization. The data presented herein are very similar compared to previous reported results in other Diptera species, strongly suggesting the occurrence of a phylogenetically conserved mechanism of follicular atresia. All these observations also support the notion that mid-oogenesis in D. oleae may be the critical regulation point at which superfluous and defective egg chambers are selectively eliminated before they reach maturity.

Histological Characteristics and Steroid Concentration of Ovarian Follicles at Different Stages of Development in Pregnant and Non-pregnant Dairy Cows

The aim of the study was to investigate the histological characteristics and steroid concentrations in follicular fluid of different populations of follicles at different stages of development, during pregnancy and the oestrous cycle in cows. Follicles from ovaries collected at a slaughterhouse were allocated into three size categories (small, 2-5.9 mm; medium, 6-13.9 mm; and large, 14-20 mm) in pregnant and non-pregnant cows. Slices were stained with HE and PAS for histological analysis. Follicular fluid was pooled according to size and pregnancy status and estradiol, testosterone and progesterone concentrations in follicular fluid were determined by RIA. Characteristics of healthy follicles did not differ, regardless of follicle size or pregnancy status. Total histological atresia was significantly higher in pregnant cows than in non-pregnant cows (p < 0.05). Estradiol increased and testosterone decreased significantly, while follicles increased in size, in both non-pregnant and pregnant cows (p < 0.05). Nonpregnant cows had the highest estradiol values in follicles of all sizes. Medium and large follicles from pregnant cows showed the lowest testosterone concentration (p < 0.05). Progesterone levels increased with follicle size only in non-pregnant animals. In large follicles, progesterone concentration was significantly higher in non-pregnant cows than in pregnant cows (p < 0.05). Considering steroid concentration and histological findings, most large follicles might be atretic during pregnancy in cattle.

The Regulation of Ovarian Granulosa Cell Death by Pro- and Anti-apoptotic Molecules

In the mammalian ovary, follicular development and atresia are closely regulated by cell death and survival-promoting factors, including hormones (gonadotropins) and intraovarian regulators (gonadal steroids, cytokines, and intracellular proteins). Several hundred thousand primordial follicles are present in the mammalian ovary; however, only a limited number of primordial follicles develop to the preovulatory stage and ovulate. The others, more than 99% of follicles, will be eliminated via a degenerative process known as "atresia". The endocrinological regulatory mechanisms involved in follicular development and atresia have been characterized to a large extent, but the precise temporal and molecular mechanisms involved in the regulation of these events have remained largely unknown. Recent studies suggest that the apoptosis of ovarian granulosa cells plays a major role in follicular atresia. In this review, we provide an overview of development and atresia of follicles, and apoptosis of granulosa cells in mammals.

Regulation of apoptosis in the atresia of dominant bovine follicles of the first follicular wave following ovulation

During atresia of bovine follicles, granulosa cells are lost through the controlled form of cell death, apoptosis. The purpose of this study was to characterize the regulation of apoptotic death of granulosa cells in dominant bovine follicles during the first wave of follicular development. Dominant follicles were collected from Holstein heifers on days 4, 6 or 8 of the first follicular wave (n = 5/day). Regulation of apoptosis in granulosa cells was examined by annexin V and propidium iodide staining; measurement of relative levels of mRNA encoding Bcl-2, Bcl-xL and Bax; and activity of caspase-3, -8 and -9. Steady-state levels of mRNA encoding four oxidative stress-response proteins were determined. Compared with day 4, the incidence of apoptotic and nonviable granulosa cells tended to increase on day 6, and numbers of nonviable cells were higher on day 8. The ratios of relative levels of mRNA encoding Bcl-2 to Bax and Bcl-xL to Bax were higher on day 6 than days 4 and 8. Activity of caspases-3 and -9 in granulosa cells did not change among the 3 days, while caspase-8 activity decreased on day 8 compared with days 4 and 6. Amounts of GSHPx, MnSOD and Cu/ZnSOD mRNA in granulosa cells were higher on day 8 than day 6. In theca interna, amounts of Cu/ZnSOD mRNA decreased between days 4 and 6. From the decreased production of estradiol and increased numbers of apoptotic and nonviable granulosa cells, we conclude that atresia of the dominant follicle is initiated between days 4 and 6 of the first follicular wave. However, apoptosis of granulosa cells does not appear to be initiated by changes in expression of oxidative stress-response proteins.

Impact of gonadotropin administration on folliculogenesis in prepubertal ob/ob mice

Female leptin deficient (ob/ob) mice exhibit abnormal ovarian folliculogenesis resulting in an impaired ability to reproduce. This effect may be related to the hypogonadotropic state of these animals, or leptin may directly modulate ovarian follicle development. In the present study we assessed whether exogenous gonadotropin administration would normalize folliculogenesis and induce ovulation in immature ob/ob animals. Eight 26-day-old ob/ob and eight control mice were injected sc with pregnant mare serum gonadotropin followed 48 h later with a sc injection of human chorionic gonadotropin. Animals were killed 24 h later. Gonadotropin (GTH) administration increased both ovarian and uterine weights in control mice, but this effect was attenuated in leptin deficient animals. The number of preantral follicles was greater in ob/ob mice than controls, but in GTH-treated animals the number of antral follicles was subnormal in the ovaries of leptin deficient animals. Ob/ob animals also failed to ovulate in response to GTH, and the protective actions of GTH against granulosa cell apoptosis and follicular atresia were attenuated in these animals. Interestingly, however, serum levels of estradiol and progesterone were higher in ob/ob mice than controls, regardless of whether or not the animals received GTH treatment. We conclude that the ovarian responsiveness to GTH is subnormal in leptin deficient animals suggesting that leptin may modulate the process of folliculogenesis by directly altering the sensitivity of the ovary to GTH.

Characterization of cyclicity and hormonal profile with impending ovarian failure in a novel chemical-induced mouse model of perimenopause

4-Vinylcyclohexene diepoxide (VCD) causes early, gradual ovarian failure in mice because it specifically targets small pre-antral ovarian follicles. The period between loss of these follicles and ovarian failure is analogous to perimenopause in women. We sought to characterize the period of onset of ovarian failure in VCD-treated mice in regard to estrous cycle length and hormonal changes. Female C57Bl/6 mice (age, 28 days) were dosed daily for 15 days with VCD (160 mg/kg intraperitoneally) to cause early ovarian failure or with vehicle only (control animals). Cycle length was monitored by vaginal cytology. Plasma levels of 17beta-estradiol (E2), progesterone (P4), and follicle-stimulating hormone (FSH) in control and VCD-treated animals were measured during proestrus of cycles 1 through 12. Cycle length (mean, 5.8 days) did not differ between groups for cycles 1 through 4. In contrast, cycle length during cycles 5 through 12 was increased (mean length, 10.9 days; P < 0.05 versus control) in VCD-treated animals, which also showed an apparent increase in plasma FSH levels. Plasma E2 and P4 at proestrus did not differ between groups during any cycle. Ovarian failure in VCD-treated mice was confirmed by histological evaluation on day 156 after onset of dosing, whereas control animals were still cycling. Therefore, despite compromised cycle length in VCD-treated mice, peak ovarian steroid production in preovulatory follicles at proestrus is adequate. These results demonstrate that the VCD-treated mouse can serve as an appropriate model to mimic hormonal changes during the perimenopausal transition in women.

Apoptosis in granulosa cells during follicular atresia: relationship with steroids and insulin-like growth factors

It is well known that during mammalian ovarian follicular development, the majority of follicles undergo atresia at various stages of their development. However, the mechanisms controlling this selection process remain unknown. In this study, we investigated apoptosis in granulosa cells during goat follicular atresia by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). The changes in the levels of steroids, insulin-like growth factors (IGFs) and IGF receptors were studied by radioimmunoassay (RIA) and semi-quantitative reverse transcription-PCR. We found that the percentage of apoptotic granulosa cells in the atretic (A) follicles was significantly higher than that in the slightly atretic (SA) and healthy (H) follicles. The level of estradiol and the ratio of estradiol to progesterone in H follicles were significantly higher than those in A follicles. On the other hand, the level of progesterone was not significantly different among these follicle types. We also found that the level of IGF-I in H follicles was higher than in SA and A follicles, whereas the amount of IGF-II did not vary significantly. The expression of IGF receptor also decreased in A follicles as compared to that in H and SA follicles. These results suggested that estradiol and IGF-I might be involved in controlling apoptosis in granulosa cells during follicular atresia.

Regulation mechanism of selective atresia in porcine follicles: regulation of granulosa cell apoptosis during atresia

More than 99% of follicles undergo a degenerative process known as "atresia", in mammalian ovaries, and only a few follicles ovulate during ovarian follicular development. We have investigated the molecular mechanism of selective follicular atresia in mammalian ovaries, and have reported that follicular selection dominantly depends on granulosa cell apoptosis. However, we have little knowledge of the molecular mechanisms that control apoptotic cell death in granulosa cells during follicle selection. To date, at least five cell death ligand-receptor systems [tumor necrosis factor (TNF)alpha and receptors, Fas (also called APO-1/CD95) ligand and receptors, TNF-related apoptosis-inducing ligand (TRAIL; also called APO-2) and receptors, APO-3 ligand and receptors, and PFG-5 ligand and receptors] have been reported in granulosa cells of porcine ovaries. Some cell death ligand-receptor systems have "decoy" receptors, which act as inhibitors of cell death ligand-induced apoptosis in granulosa cells. Moreover, we showed that the porcine granulosa cell is a type II apoptotic cell, which has the mitochondrion-dependent apoptosis-signaling pathway. Briefly, the cell death receptor-mediated apoptosis signaling pathway in granulosa cells has been suggested to be as follows. (1) A cell death ligand binds to the extracellular domain of a cell death receptor, which contains an intracellular death domain (DD). (2) The intracellular DD of the cell death receptor interacts with the DD of the adaptor protein (Fas-associated death domain: FADD) through a homophilic DD interaction. (3) FADD activates an initiator caspase (procaspase-8; also called FLICE), which is a bipartite molecule, containing an N-terminal death effector domain (DED) and a C-terminal DD. (4) Procaspase-8 begins auto-proteolytic cleavage and activation. (5) The auto-activated caspase-8 cleaves Bid protein. (6) The truncated Bid releases cytochrome c from mitochondrion. (7) Cytochrome c and ATP-dependent oligimerization of apoptotic protease-activating factor-1 (Apaf-1) allows recruitment of procaspase-9 into the apoptosome complex. Activation of procaspase-9 is mediated by means of a conformational change. (8) The activated caspase-9 cleaves downstream effector caspases (caspase-3). (9) Finally, apoptosis is induced. Recently, we found two intracellular inhibitor proteins [cellular FLICE-like inhibitory protein short form (cFLIPS) and long form (cFLIPL)], which were strongly expressed in granulosa cells, and they may act as anti-apoptotic/survival factors. Further in vivo and in vitro studies will elucidate the largely unknown molecular mechanisms, e. g. which cell death ligand-receptor system is the dominant factor controlling the granulosa cell apoptosis of selective follicular atresia in mammalian ovaries. If we could elucidate the molecular mechanism of granulosa cell apoptosis (follicular selection), we could accurately diagnose the healthy ovulating follicles and precisely evaluate the oocyte quality. We hope that the mechanism will be clarified and lead to an integrated understanding of the regulation mechanism.